Ultraviolet water treatment apparatus

ABSTRACT

An ultraviolet water treatment plant is provided in which individual ultraviolet lamp units are loosely and retractably located within frames supported in a water treatment channel. Individual frames supporting arrays of parallel lamp units may be removed from the channel, and the lamp units may be individually disengaged from the frame and disassembled for lamp replacement. The frames have unitary plug connectors to a power supply arranged so that the plug of a frame must be disengaged from the supply before that frame can be removed from the channel. The level of water in the channel is controlled according to the rate of flow, and the lamp units are selectively energized according to whether they are immersed so as to match the irradiation provided to the rate and cross section of the flow.

FIELD OF THE INVENTION

This invention relates to ultraviolet water purification systems.

BACKGROUND OF THE INVENTION

For many years, the most widely used technique for purifying largequantities of water has been the addition of small quantities ofchlorine or chlorine releasing compounds to the water, sufficient todestroy undesirable micro-organisms. Chlorination has however thedisadvantages firstly that it tends to render the water less acceptablefor drinking or bathing, particularly if the chlorine concentration andpH of the water are not carefully controlled, and secondly that thechlorine may interact with other compounds present in the water to leavelow concentrations of possibly harmful chemicals.

It has been known for many years that ultraviolet light at appropriatewavelengths has powerful germicidal properties, and the use ofultraviolet light for water purification purposes has been gaining inpopularity in recent years since it avoids the disadvantages associatedwith chlorination. The problems associated with such treatment aremainly problems of implementation, i.e. ensuring adequate irradiation oflarge quantities of water in an effective and energy efficient manner,using equipment which is readily and economically maintained.

One type of equipment which has found favour uses a battery of parallelelongated ultraviolet tubes supported on appropriate carrier frames in achannel through which the water to be treated is caused to flow. Thespacing of the tubes from each other and from the walls of the channelis such as to minimize the path of the ultraviolet radiation from thetubes through the water. An example of such an arrangement is shown inU.S. Pat. No. 3,948,772.

As the number of tubes utilized in an installation increases, it becomesincreasingly essential that adequate provision be made for replacingtubes as and when they fail. One approach to this problem is disclosedin U.S. Pat. No. 4,482,809 (Maarschalkerweerd) issued Nov. 13, 1984.This patent discloses an arrangement in which groups of verticallyadjacent tubes are supported in individual rack assemblies which can bewithdrawn from a treatment channel for replacement of tubes. In thearrangement described in this patent, the lamps are housed intransparent tubes extending between sockets integral with the side armsof a rigid frame, at least one of the sockets having an end plug throughwhich a lamp can be withdrawn longitudinally once the frame has beenwithdrawn from the channel. This arrangement is relatively complex tofabricate, and while it may appear an advantage that the lamps arerigidly secured in the frame, this entails that any distortion of theframe during handling strains the quartz tubes containing the lamps,thus risking breakage. Furthermore, considerable attention must be paidto leak-proofing, since any leak may penetrate throughout the assembly.

A further problem with such assemblies is that they are commonlyrequired to accommodate widely varying rates of water flow, which meansthat the degree of irradiation will vary according to the rate of flowunless some means is provided to compensate for this effect.

Finally the use of electrical equipment in a wet environment, and theuse of high intensity ultraviolet radiation, poses safety hazardsagainst which the operators of the plant should be protected. Inparticular, there should desirably be some positive assurance that poweris disconnected from the assemblies before they can be removed from thechannel, since this both inhibits disassembly in a powered up condition,and ensures that radiation ceases before an assembly is removed.

It is an object of the present invention to tackle the above problems.In a first aspect, the present invention provides in a water treatmentplant comprising a treatment channel for the passage of water to betreated, at least one array of parallel elongated ultraviolet electriclamp units, means for supporting said at least one array with thechannel, and means for connecting said array to an electrical powersupply, the improvement wherein each lamp unit in the array comprises anindividually watertight assembly of a tubular ultraviolet lamp, atubular housing for the lamp which is transparent to ultravioletradiation, and watertight end cap units for the tube, at least one beingremovable and which establish electrical connections to the lamp, andthe lamp units are assembled into arrays by releasably engaging theassembled units between end bars of a frame, said end bars releasablyengaging opposite end caps of each assembled unit. Preferably the endbars have series of spaced sockets between which the lamp units areremovably located, each end cap of a lamp unit comprising a locatingspigot releasably engageable with locating means on an end bar so as torequire removal of that end cap from the frame before the lamp unit canbe disassembled.

The end bars may be connected by braces extending parallel to the lampunits to provide a frame which may be suspended from spaced hangers of arack supported above the channel. Preferably the frame mounts a multipleconnector plug establishing electrical connections between the lamp anda complementary socket mounted on the rack and connected to the powersupply, such that the frame cannot be removed from the rack withoutwithdrawing the plug from the socket. In a preferred arrangement, theframe must be moved horizontally on the rack to disengage the plug fromthe socket before it can be lifted upwardly from the channel.

The invention also extends to the provision of, in an ultraviolet watertreatment plant comprising a treatment channel for the passage of waterto be treated, at least one vertically stacked array of elongatedultraviolet electric lamp units, means for supporting said at least onearray within the channel, and means for connecting the lamps of saidarray individually to a power supply, the improvement wherein means areprovided to restrict the flow of water through the channel such that thedepth of water in the channel, and hence the number of lamps in eachsaid array which are immersed, is progressively increased in accordancewith the rate of flow through the channel, means to sense the depth ofwater in the channel, and switching means associated with said powersupply and controlled by said sensing means to turn on only such lampsas are required to irradiate the water.

Preferably the means to restrict the flow of water through the channelcomprises a weir assembly comprising an upper barrier portion, spanningthe channel, and having an upper edge forming a weir, and a lower sluiceportion hingedly suspended from the lower edge of the upper barrier forswinging movement in a downstream direction and biased towards aposition in which it closes the channel beneath the upper barrier. Asthe water level upstream of the weir assembly increases the sluicefirstly opens progressively to permit an increasing flow of water, andthen the rate of flow through the fully opened sluice increases as thelevel of water behind the barrier increases. Finally the water poursover the weir at increasing rates as its level further increases.

Further features of the invention will become apparent from thefollowing description of a preferred embodiment with reference to theaccompanying drawings.

IN THE DRAWINGS

FIG. 1 is a side elevation of a plant in accordance with the invention;

FIG. 2 is a section on the line 2--2 in FIG. 1;

FIG. 3 is a side elevation on an enlarged scale of a single lamp array;

FIG. 4 is an end elevation showing two arrays as shown in FIG. 2;

FIG. 5 is a perspective view on an enlarged scale illustrating themounting of an individual lamp unit to end bars of the array of FIG. 4;

FIG. 6 is a sectional view of an end cap of a lamp unit and adjacentparts;

FIG. 7 is a fragmentary longitudinal section on the line 8--8 in FIG. 8through a portion of the channel of the plant, showing a level controldevice; and

FIG. 8 is a transverse section through the channel, also showing thelevel control device.

Referring to FIGS. 1 and 2, the apparatus comprises a stainless steelchannel 2 having inlet and outlet pipes 4 and 6 at opposite ends and ofa capacity sufficient to handle the maximum anticipated flow of waterthrough the apparatus without significant restriction. Although the unitshown is free-standing, it may be more convenient, especially in largeunits, to form the channel in the ground and provide it with a suitableliner. It is desirable that the liner has a highly reflective surface soas to maximize irradiation effectiveness, and stainless steel is apreferred material because of its ability to maintain a specular surfacein potentially corrosive conditions.

Within the channel are located one or more banks (only one is shown) ofarrays of ultraviolet lamp units 8 each supported on a rack formed bytransverse rails 10. At the downstream end of the channel is a levelcontrol system comprising a weir assembly 12 and level sensor assembly14. A power supply and control console unit 16 is provided adjacent thechannel, which is provided with top covers 18 which are removable formaintenance, but normally prevent the escape of ultraviolet radiation orthe ingress of foreign matter.

Referring to FIGS. 3 to 5, the individual lamp arrays 8 comprise anumber, in this case four, of vertically stacked parallel horizontaltubular lamp units 20 located by end bars 22. The end bars 22 areinterconnected by horizontal cross members, of which an upper crossmember 24 is tubular and extends outwardly of the bars 22 to providesupports which rest on the rails 10. Flexible insulated wires 26 for thelamp units 20 enter the tubular member 24 and are connected to the pinsof a multiple conductor plug 28 mounted on one end of the member 24 sothat by bodily longitudinal horizontal movement of the array on thecross members 10, the plug may be moved into or out of engagement withone of an array of sockets 30 (see FIG. 1) connected to the power supplyunit 16 by conductors passing through a conduit 32. The lower crossmember is positioned above the highest anticipated water level in thechannel, and is an inverted channel shaped stainless steel plate whichperforms the dual function of bracing the frame, and reflecting backinto the channel radiation which would otherwise escape upwardly to thedetriment of both operating efficiency and the safety of personnelremoving lamp arrays for maintenance.

The lamp units 20 are not rigidly attached to the bars 22 of the frame.Instead, the units have end caps 34, described in more detail below,provided with axially outwardly extending spigots 40 which arereleasably captive within locating apertures 36 and 38 in the bars 22,as best seen in FIG. 5. One bar 22 is formed with a series of roundapertures 32 to receive the spigots 40 at the one ends of the lamp unitsat appropriate levels. The other bar is formed at corresponding levelswith slot like apertures 38 through each of which the spigot 40 at theother end of a lamp unit may be moved upwardly and laterally out ofengagement with the bar, after which the spigot 40 at the first end maybe moved longitudinally out of engagement with the associated aperture36. Unintended disengagement of the pin 40 from the slot 28 is preventedby insertion of a split pin 42 through the bar 22 to hold the pin withinthe downwardly extending portion of the slot. Gravity alone cannot berelied upon to retain the pin in the slot since the lamp units will tendto float once submerged. It should be noted that the bars 22 merelyserve to locate the lamp units in their proper position, and once anassembly 8 is removed from the channel (thus interrupting the supply ofpower to the tubes), the split pin 42 retaining any lamp unit can beremove and one or more ends of the unit withdrawn from the frame to theextent permitted by the flexible supply cables 26; only then can it bedisassembled for lamp replacement or other maintenance, since otherwisethe spacing between the bars 22 ensures that the end caps must be fullyengaged with the remainder of the units.

The construction of lamp units is shown in more detail in FIG. 6. Theunit comprises a tubular lamp 44 emitting ultraviolet radiation ofsuitable wavelength, typically 2540 Angstroms, housed within a quartztube 46 transparent to such radiation and of the type conventionallyutilized to protect such lamps. Electrical connections to each end ofthe tube are established by means of conventional press-on connectors 48within housings slidable within the tube 46 and urged against the tubeby springs 50 mounted on spigots 52 at the inner end of an axiallyextending core 54 of the end caps 34. Each end cap, which may be mouldedin one piece from synthetic plastics material, has an external sleeve 56surrounding an end of the tube 46 and the core 54 has deformableperipheral ribs which establish a watertight seal to the tube 46. Theflexible cable 26 passes through and is sealed to the plug 26 on its wayto the cap 48. The lamp 44 may be easily replaced once the lamp unit isremoved from the array simply by pulling the end caps 34 off the tube 46and the connectors 48 off the lamp 44. A new lamp may then be placed inthe tube 46 and the caps replaced, prior to re-engaging the re-assembledlamp unit with the bars 22, replacing the lamp array 8 in the channel 2so that the tubular member 24 rests on the rack formed by the crossmembers 10, and moving the array longitudinally of the channel tore-engage the plug 28 with the associated socket 30.

The total number of lamp units 20 in the several arrays 8 is of coursefixed for any particular installation, but the flow of water to betreated may vary over a wide range. With low rates of flow, operation ofthe total number of lamp units would lead to unnecessarily high levelsof irradiation and resultant waste of energy. In order to mitigate thisproblem, provision is made to regulate the depth of water in the channelaccording to the rate of flow so as to immerse differing numbers of lampunits, and to sense the depth so that only those lamps which areimmersed will be energized, thus conserving energy and prolonging thelife of some of the lamps. The flow of water is regulated by means ofthe weir assembly 12, and the level of the water within the channel issensed by the sensor array 14, which are described in more detail withreference to FIGS. 7 and 8.

The weir assembly comprises a barrier 60 spanning the channel and a flap62 connected to the lower edge of the barrier 60 by hinges 64. The flapis biased to a position closing a gap beneath the barrier 60 by a biasweight 66. A baffle 68 prevents water pouring over the barrier 60 fromfalling onto the flap 62. When water is flowing through the channel at alow rate, its exit will be restricted by the flap 62 until the waterrises to a level sufficient to cause opening of the flap against thebias applied by the weight 66. This level is selected to be high enoughto ensure submersion of at least the lowest lamp unit 20 in each array8, and normally only these units will be energized by the power supplyunit 16. As the rate of flow in the channel increases, the flap willopen more fully to accommodate the flow until the barrier 60 becomes anobstacle to flow. The level will then rise behind the barrier as theflow rate further increases, until ultimately the water will pour overthe weir formed by the top of the barrier. As the water level rises, itwill successively contact the bottom of the level sensing probes 70, 72and 74, each of which will signal to the control and power unit 16 thatanother lamp unit in each array has been submerged and can be turned on.Thus when the flow through the system is less than a certain minimum,only one in four (in the example shown) of the lamps will be turned on,with additional lamps being switched on as the rate of flow and thecross section of the flow increases, providing for adequate yeteconomical treatment for a wide range of rates of flow. This feature isparticularly valuable in systems for storm water treatment, where ratesof flow may vary very widely and rapidly, whilst being minimal or zerofor much of the time. An additional sensor to switch the lowest tier oflamp units may of course be provided if conditions require this.

Although not shown, ultraviolet sensing devices are provided in thechannel to monitor the radiation level therein and verify that this issufficient to provide a required degree of sterilization. The passage ofcurrent through individual lamps is also monitored so that failed lampscan be detected and then replaced as previously described.

Although in the embodiment described, the lamp units extendlongitudinally in a single bank of arrays, other arrangements arepossible. Thus two banks could be provided in series to provide enhancedperformance, or the arrays could be arranged and supported so that thelamp units extend transversely or vertically in the channel.

Rather than providing for lamp units which can be disassembled on site,the end caps may be more or less permanently sealed to the quartz tubes,and the cables to the lamp units may be provided with connectors 27 sothat the entire unit can be replaced.

We claim:
 1. In a water treatment plant comprising a treatment channelfor the passage of water to be treated, at least one array of parallelelongated ultraviolet electric lamp units, means for supporting said atleast one array within the channel, and means for connecting said arrayto an electrical power supply, the improvement wherein each lamp unit inthe array comprises an individually watertight assembly of a tubularultraviolet lamp, a tubular housing for the lamp which is transparent toultraviolet radiation, and watertight end closures closing both ends ofthe tubular housing through which closures pass cables establishingelectrical connections to end caps on the lamp, and wherein the lampunits are assembled into arrays by releasably capturing the assembledunits between end bars of a frame, said end bars beign separate from andreleasably engaging opposite end closures of each assembled unit.
 2. Awater treatment plant as claimed in claim 1, wherein the end bars haveseries of spaced sockets between which the lamp units are removablylocated, each end closure of a lamp unit comprising a locating spigotassembly releasably engageable with locating means on an end bar so asto require removal of that end closure from the frame before the lampunit can be disassembled.
 3. A water treatment plant as claimed in claim2, wherein the end closures are a press fit on the tubular housing.
 4. Awater treatment plant as claimed in claim 2, wherein the lamp unitsextend horizontally, and the end bars extend vertically, and thelocating means in one end bar are holes receiving the spigots on the oneend closures of the lamp units in an array, and the locating means inthe other end bar are slots into and out of which the spigots of theother end closures of the lamp unit in the array can be manoeuvered. 5.A water treatment plant according to claim 1, wherein the end bars areconnected by braces extending parallel to the lamp units to provide aframe which may be suspended from spaced hangers of a rack supportedabove the channel.
 6. A water treatment plant according to claim 5,wherein the frame mounts multiple connector plug establishing electricalconnections between the lamps and a complementary socket mounted on therack and connected to the power supply, such that the frame cannot beremoved from the rack without withdrawing the plug from the socket.
 7. Awater treatment plant according to claim 6, wherein the frame is movablehorizontally on the rack to disengage the plug from the socket.
 8. Awater treatment plant according to claim 1, wherein the end closures arepermanently sealed to the tubular housings, and the cables establishingelectrical connections to the end caps on the lamps have releasableconnectors so that each lamp unit may be individually replaced as aunit.
 9. A water treatment plant according to claim 1, wherein the endclosures each comprise a watertight deal in an end of the tubularhousing, and external sleeve surrounding said end of the tubularhousing.